I have a few box fans filters and one cuboid fan, it's not actually the cuboid though, I used a circular hepa filter with the inline duct booster fan. I leave

I have a few box fans filters and one cuboid fan, it's not actually the cuboid though, I used a circular hepa filter with the inline duct booster fan. I leave the fan duct fan running on low (right at the midpoint of the speed dial so technically medium I guess) 24/7 in my kitchen out of eye site because it's so quiet. So, in my experience, much quieter, quiet enough that people don't notice it running all the time. I have the dial in reach though so I can crank it all the way if something burns on the stove, clears the air out shockingly fast. I got some sound proof panels and crappily bungee corded them around the fan and it didn't have a noticeable effect. I think if I put more effort into the sound baffles it would reduce the sound, but the whole setup without baffles is quiet enough I haven't bothered.